Parkinson's law - I think it appeared in The Economist originally, but I can't be bothered to look it up - stated that "work expands to fill the time available for its completion".

The automotive update of this is that the number of cars expands to fill the road available. This is as it should be, since a road with no car on it is, temporarily, a bit of a waste of tarmac. It has to be there for when the car comes along, but until it does come along, it's like cheese in the fridge. Not fulfilling its proper function of becoming cheesy sauce.

Now some people have strange ideas about all this. When the M25 was opened, it immediately filled with traffic and a lot of people pointed to this as a sign of failure in transport planning. "It's only just opened," they would wail, "and now look at it. Full of cars." That's a bit like complaining that Top Gear Live has sold out, which we obviously wouldn't do, even if it did.

Really, if the M25 had filled up with stray cattle, it would have been a complete waste of money. Beer is for drinking, money is for spending and roads are for driving on. More people driving around doing more stuff is good for what once used to be called UK plc*.

Now look, I realise that out in the sticks you can drive for miles and miles before coming across an old Morris driven by someone who's amazed that cars have radios these days. But the roads in the countryside are really only there to allow yokels like Richard Hammond to drive into the city occasionally and point in awe and wonder at the electric lightbulbs. In the cities, the roads are full.

I live in London, and I've been doing quite a bit of driving around it this week, during the busy times. My conclusion is that the roads are operating exactly at capacity. There is not room for one more car, and removing just one parking space would bring the place to a standstill. Excellent. Maximum capacity management. If it were a mobile phone factory, the board of directors would be delighted.

But there is a downside to all this. It only takes one tiny stoppage to ruin everything, and that brings me to the subject of breakdowns.

The way in which cars break down is a subject worthy of a PhD, and maybe one has been done. I was once in a car with Hammond that took so long to expire that there was time for a heated debate about what the problem was before we came to a complete halt. I thought it was electrical; he thought it was fuelling. As it turned out, the main problem was that it was a car owned by Richard Hammond.

When my first 911 went, on the A4 into west London, it died as instantly as a man at the epicentre of a nuclear explosion. It was going, then it wasn't. But this is a bit academic to the point I'm trying to make here. Both cars became, quite literally, clots.

Complete breakdowns in modern cars are quite rare, but they do happen. I've seen two, on very busy roads, in the last two days. At each scene, there were traffic wombles putting out cones and recovery trucks trying to fight their way through the massive car park that resulted. We really don't have time for this rubbish.

So here's my plan for May's Britain. When a car breaks down somewhere like London, Manchester or Edinburgh, any other driver will be able to ring a distress hotline. The recovery helicopter is then scrambled. It will be something quite big, with a massive grabber suspended below it.

If the broken car hasn't moved on by the time the chopper arrives, it will be picked up and dumped in the river.

And I don't care if it's a Veyron Super Sport or a carbon-fibre Lamborghini. It doesn't matter how valuable it is; it isn't as valuable as the collective time being lost to everyone else. People have bookings at fashionable restaurants, and I have to get to the tool shop.

Sounds harsh? It is a bit, but you'll be able to opt in or out of grab 'n' dump insurance, which will be weighted according to the sort of car you have and how well you look after it. It'll certainly make people think. In May's Britain, you'd hesitate before driving into

London in a classic car or anything not wired up by Germans. But so you should.

It'd be downright irresponsible.

*By Lord Young of the DTI during the Thatcher era, if I remember rightly